English Amiga Board - View Single Post - Horizontal Scrolling with 4x Fetch and all sprites

roondar · 04 December 2018, 23:03

One thing I have considered, but not programmed/tried yet is a 'partial' approach where you use the standard $38 ddfstrt and use a display window that is shifted by 16 or 32 pixels to the right.

Then, using 4x fetch it should be possible to scroll by either 16 or 32 pixels using the hardware without odd effects (using a delay of the right values to only shift this many pixels without showing empty space). This then gives you 16 or 32 frames to create a 16 or 32 pixel shifted version of the screen in a new bitmap buffer.

This might work. It will take a whole bunch of memory though (2 additional full screen buffers) and I've not calculated to see if the extra Blitter/CPU cost of drawing the screens this way is actually smaller than the gains for 4x fetch mode.

Edit: did a bit of back-of-the-envelope calculation and it seems that this method probably does not gain you any time. It probably won't lose you any either, but meh - not super useful.

04 December 2018, 23:03	#5
roondar Registered User Join Date: Jul 2015 Location: The Netherlands Posts: 3,423	One thing I have considered, but not programmed/tried yet is a 'partial' approach where you use the standard $38 ddfstrt and use a display window that is shifted by 16 or 32 pixels to the right. Then, using 4x fetch it should be possible to scroll by either 16 or 32 pixels using the hardware without odd effects (using a delay of the right values to only shift this many pixels without showing empty space). This then gives you 16 or 32 frames to create a 16 or 32 pixel shifted version of the screen in a new bitmap buffer. This might work. It will take a whole bunch of memory though (2 additional full screen buffers) and I've not calculated to see if the extra Blitter/CPU cost of drawing the screens this way is actually smaller than the gains for 4x fetch mode. Edit: did a bit of back-of-the-envelope calculation and it seems that this method probably does not gain you any time. It probably won't lose you any either, but meh - not super useful. Last edited by roondar; 04 December 2018 at 23:14.